This is an interesting idea. Essentially its a bigger, hires screen and keyboard for your Windows Mobile device.
You connect it to your smartphone and it displays your smartphone screen on the Redfly's WVGA screen and allows accessing programs and documents through the Redfly. The first thing to wonder with this device is - will your applications scale correctly to 800x480? Fortunately there are a few WVGA devices already on the market so the answer: with most newer applications should be "yes".
This is a very similar idea to the Foleo for Palm devices. The Foleo never made it to market - likely due to the decline in Palm market share and the high price point of $499. http://en.wikipedia.org/wiki/Palm_Foleo
As someone that enters a lot of data into my phone I could see the use in this. But really - I think I'd rather get a mini-notebook like the Asus Eee PC and use Dashwire's software (athough that requires an active internet connection).
I imagine the Redfly is a product you'll have to try before passing judgement. If its extremely easy to use it might justify the $200 US for the entry model. But at that price I'm not quite interested enough to find out.
I do love products like this and I hope they have a market. Less tech savy road warriors might find this indispenable (again - if its dead simple to use).
And finally a link to back to My Today Screen who posted the first article I had read on the Redfly.